The country's two-tiered economy - growth in the non-resource cities against a decline in Perth and Brisbane - has been emphasised in the national office vacancy data, which has continued to climb into double digits.

This is against the backdrop of rents hitting more than $1600 a square metre in Sydney and about $1300 a square metre in Melbourne for premium skyscrapers, and against the number of landlords of premium and A-grade office towers consolidating following the takeover of the Commonwealth Property Office Fund by the Dexus Property. GPT and Dexus are now considered Australia's two biggest office landlords.

According to the Property Council of Australia's (PCA) office market vacancy numbers for the six months ending in January, the national vacancy rate grew to 10.4 per cent, up from 10.1 per cent reported in July.

A breakdown shows Sydney rose from 8.9 per cent to 9 per cent due to new supply coming on stream from developments including Barangaroo, the exhibition and convention centre project and Grocon's Ribbon site (the Imax theatre) at Darling Harbour, and redevelopments along Martin Place.

In contrast, Melbourne saw a drop from 9.8 per cent to 8.7 per cent due to companies expanding into new developments. For the first time in its history, Southbank has the ''no vacancy'' sign on display.

But to the north and west, the story is different, with Brisbane's vacancy rate rising from 12.8 per cent to 14.2 per cent, and Perth's up from 6.9 per cent to 9 per cent.

PCA chief executive Peter Verwer said Australian office markets were in transition.

''The increase in average vacancies and historically low demand reflect lacklustre economic growth over four of the past five years,'' Mr Verwer said.

''Demand in Brisbane and Perth, in particular, have directly tracked declining resource prices.''

There was some easing in pressure on the eastern seaboard, with obsolete office blocks in Sydney and Melbourne being converted into residential towers. Real estate agents say that conversion trend will continue for the next year.

Companies are also eyeing the air space above their properties. David Jones, for example, is contemplating the construction of apartments above its Market Street store.

The PCA's NSW executive director, Glenn Byres, said signs of life were returning to Sydney's city market, but he added that the increasing demand did not offset new supply.

The NSW head of leasing at Jones Lang LaSalle, Tim O'Connor, said Sydney was a beneficiary of the economic transition from investment-led growth in the mining sector to more broad-based domestic consumption and investment drivers.

Matt Whitby, Knight Frank's national director of research, said all major city-centre office markets in Australia recorded negative absorption (net leasing) and declining ''effective'' rents during 2013.

''With the supply pipeline in most markets benign over the next two years, there will be the commencement of downward pressure on vacancy rates in 2014,'' he said.